Apparatus for mixing fluids



y 4, 1960 B. H. THURMAN 2,937,857

APPARATUS FOR MIXING FLUIDS Filed Jan. 12, 1956 2 Sheets-Sheet 1 w 4 I6 32 A ATTORNEYS 5i y 1960 B. H. THURMAN 2,937,857

APPARATUS FOR MIXING FLUIDS Filed Jan; 12, 1956 2 Sheets-Sheet 2 IN VENTOR 5611mm [1. 7210mm BY 16% W ATTORNEYS United States Patent APPARATUS FOR MIXING FLUIDS Benjamin H. Thurman, New York, N.Y., assiguor to Benjamin Clayton, doing business as Refining, Unincorporated, a sole roprietorship Filed Jan. 12, 1956, Serial No. 558,718

20 Claims. (Cl. 259-9) This invention relates to an apparatus for mixing fluids, and more particularly to an improved apparatus for dispersing alkaline refining agents into a glyceride oil, such as an animal or vegetable oil, in order to facilitate intimate contact of the alkaline reagent with the impurities in the oil without appreciable attack upon the oil itself and without formation of stable emulsions.

In the processing of glyceride oils, it is frequently necessary to remove coloring matter and/or materials which impart to the oil a deleterious taste or odor. According to processes well known in the refining art, relatively strong caustic solution is mixed with the oil to form an emulsion which, after sufiicient time has elapsed or chemical reaction of the alkali, is then broken so that the mixture may be separated. Such treatment may take place as the second stage of a refining process wherein either caustic soda or soda ash has been used in the first refining stage to remove the bulk of the fatty acids and gums.

An example of a glyceride oil which requires color removal is a cottonseed oil which has been refined with non saponifying alkalies such as soda ash or with caustic alkali which, because of its low concentration .or insufiicient quantity, has failed to lower the color of the oil to the required extent. The conventional refining operation with either of these alkali reagents adequately removes the free acid content, and also removes substantially all of the gums, but the resulting oil is usually of a darker color than desired. It is therefore necessary to re-refine the oil using a small amount of a caustic alkali of relatively high concentration or a similar color-reducing material to produce a low colored oil.

Many methods for dispersing the strong caustic solution into the oil have been suggested, varying from continuous methods in which the caustic solution is said to be instantaneously dispersed into the oil, to batch methods in which the oil is subjected to violent agitation for a period of 5 to 30 minutes by impellers which may be driven at speeds up to 5000 rpm. None of these methods, however, are entirely satisfactory from the standpoint of degree of color removal, recovery of oil, and/or overall economy and ease of operation. 7

Thus, the conventional, co'ntinuous mixture methods and apparatus, while satisfactory for the first step of re fining wherein fatty acids and gums are removed, may not be adequate to effect sufficient contact of the strong caustic with the coloring matter in the oil to cause the desired degree of decolorization in a re-refining opera-v tion. On the other hand, the batch methods depending on longer mixing times and/or high impeller speeds, in some instances actually producing a so-called shearing of the oil, invariably are accompanied by relatively high re-refining losses which may be due to saponification of some of the glyceride content of the oil and/or formation of emulsions from which the oil can be recovered only with difiiculty. Oil losses in such processes are seldo'rn less than about one percent and often run much higher. Moreover, such processes require a relatively high ex- 2,937,857 Patented May 24, 1960 penditure of energy in relation to the amount of re-refined oil produced.

The present invention solves these ditficulties by providing an improved continuous mixing operation and apparatus whereby the caustic is extensively and substantially instantaneously dispersed throughout the oil with relatively high -flow rate and minimum expenditure of energy, but without either substantial homogenizing or shearing action, so that the caustic is available to act upon the impurities in such oil while avoiding the formation of a stable emulsion and saponification of any substantial quantity of the glyceride content of the oil. Oil losses in re-refining processes utilizing the mixing apparatus of the present invention are low, for example, in the order of 0.2% to 0.4% or less.

Accordingly, an object of the present invention is to provide an improved apparatus for intimately dispersing reagent substantially instantaneously throughout an oil medium. 7

Another object of the invention is to provide an appa ratus for intimately dispersing caustic solution through out an oil without substantial homogenizing or shearing action upon the oil.

Another object of the invention is to provide an apparatus for dispersing reagent into glyceride oils containing only a small amount of impurities, in which the refining losses are reduced. I v

A still further object of the invention is to provide an improved apparatus for reducing the color of refined glyceride oils by chemicaltreatment, with very little re fining loss.

Another object of the invention is to provide an appa ratus for dispersing alkali solution in oils with a minimum expenditure of energy.

Yet another object of the invention is to provide an improved mixing apparatus for substantially instantaneously dispersing at least one liquid in another without subjecting such liquids to shearing and emulsification.

In accordance with the improved methods of mixing of the present invention, proportioned streams of the fluidsto be mixed, such as streams of oil and alkali, are combined and the resultant combined stream is forced at a relatively high rate of speed along a confined path in contact with a series of inclined surfaces staggered in suchmanner as to subject the combined oil-caustic stream to traverse flow with respect to the general direction of fiowalong said confined path and to rapid reversal of direction of such traverse flow asthe fluid stream is generally advanced along said path, whereby the mixing action causes a rapid and substantially instantaneous dispersion of the caustic throughout the oil without subjecting the moving liquid mass to substantial shearing actionthereby avoiding substantial homogenization or saponification of the oil. In order to provide still further mixing action, the moving stream may be contacted with additional sur faces along the confined path which surfaces are spaced from said staggered surfaces and are inclined in thegen eral direction of the flowing mass. The resultant stream, after a residence time in said confined path of only about one or two seconds, or, in some instances, only a fraction of a second, is then heated or subsequently treated in conventional manner to facilitate reaction of the impurities of the oil with the dispersed caustic, whereupon the reacted mixture may be separated by centrifugal ac tion in a known manner. I

For a further description of the apparatus of the pres ent invention, and of the objects and advantages thereof,

apparatus utilized in carrying out the process of the in vention;

Fig. 2 is an end view of the mixer shownin Fig. 1;

Fig. 3 is an enlarged fragmentary cross-sectional view of the mixing apparatus taken along the line 33 of Fig. 2 and looking in the direction of the arrows;

Fig. 4 is an enlarged sectional view of the mixing apparatus taken along the line 44 of Fig. 3, and showing the construction of a dividing wall separating the apparatus into plural mixing chambers;

Fig. 5 is an enlarged sectional view of the mixing apparatus taken along the line 55 of Fig. 3, and showing the construction and arrangement of a first mixing chamber and impeller therein;

Fig. 6 is an enlarged fragmentary sectional view of a portion of the dividing wall of the mixing apparatus taken along the line 66 of Fig. 4, and showing the configuration of one set of inclined mixing grooves in such wall;

Fig. 7 is an enlarged fragmentary cross-sectional view of another portion of the dividing wall. of the mixing apparatus taken along the line 77 of Fig. 4, and showing the configuration of a second set of mixing grooves;

Fig. 8 is a perspective view of the mixing impeller shown in assembly in Fig. 5 and in the first or left mixing chamber in Fig. 3;

Fig. 9 is a perspective view of the impeller shown in the second mixing chamber of the assembly of Fig. 3; and

Fig. 10 is an enlarged fragmentary perspective view of a portion of the periphery of one of the mixing chambers of the mixing device showing one of the means for effecting mixing action.

Referring now to the drawings in detail, there is shown in Fig. 1 a mixer of cylindrical configuration generally indicated by numeral 10, comprising a plurality of housing sections including a cover plate and bearing assembly 12, a first impeller housing member 14, a second impeller housing member 16, and an end plate 18. The cover plate and bearing assembly 12 includes a motor housing portion integral therewith and provided with a mounting bracket 22 having a flange 24 thereon which may be bolted or otherwise afiixed to any desired base whereby to support the entire mixer assembly. The motor housing section 20 contains an electric motor of an output capacity selected in accordance with the size and power requirements of the mixer 10. Such motor may be adapted to develop shaft speeds of for example 1740 r.p.m. or 3400 r.p.m. The motor and mixer are provided with a common shaft 26, which is shown projecting from the left side of the motor housing 20 as viewed in Fig. 1. It will be understood that the mixer may be mounted by other suitable means and that the mixer shaft may be driven by other suitable power sources. However, the device as shown with the integral motor housing and motor provides a very compact and desirable unit.

A bafile or dividing wall member 28, which will be further described hereinafter, is interleaved between the housing sections 14 and 16. Each of the housing members 12, 14, 16, and 18, and the baflle member 28 is provided with a plurality of bolt holes adjacent the periphery thereof, which in the assembled structure provide registering openings adapted to receive bolts 30 which by virtue of nuts 32 hold these sections in closely assembled relationship.

The material of which the housing sections and baflie member are fabricated is preferably one resistant to corrosion by the alkali reagent and not subject to attack by the oil. Cast iron has been utilized for these parts, but it will be understood that other corrosion-resistant metals or alloys, as well as certain plastic materials might be employed.

Referring now particularly to Fig. 3, it will be seen that the impeller housing members 14 and 16 are of. annular configuration and in co-operation with the inner;

faces of cover plate 12, baflle 28, and end plate 18, provide a pair of mixing chambers designated as 34 and 36 respectively. The cover plate 12 is provided with an axial bore 38 which forms a bearing for one end of the motor and mixer shaft 26. The shaft 26 extends into mixing chambers 34 and 36, and carries thereon a pair of rotors or impellers 42 and 44. The cover member 12 is further provided with an inwardly extending axial boss 46 which is adapted to fit into a counterbore 48 formed within the hub 49 (Fig. 8) of the impeller member 42. The counterbore 43 contains a sealing assembly including from right to left, as viewed in Fig. 3, a gasket 50 of Teflon or other anti-friction material which is substantially unaifected by the action of alkali or oil, a steel ring 52, a carbon ring 54, a shaft seal 56 of Teflon or the like having a recessed end, a retaining collar 58, also of Teflon or the like, which fits over the recessed end of shaft seal 56 to provide a shoulder portion 60, and a compression spring 62, one end of which bears against shoulder 60 and the other end of which bears against a collar 64 in contact with the bottom face of the counterbore 48 of the impeller 42. It will be seen that the spring 62 thus urges the sealing members in the direction of the boss 46 of the cover plate 12, thereby effectively sealing the chamber 34 against leakage along the shaft 26. The gasket 50 and steel ring 52 tend to remain stationary while the remaining parts of the seal assembly rotate with the shaft 26. The relative movement is therefore between steel ring 52 and carbon ring 54, and very little frictional loss is introduced by reason of such seal. It will be understood, however, that other conventional shaft-sealing means may be employed.

The baffie or partition Wall 28 between chambers 34 and 36 has a central bore 66 which is adapted to receive and form a bearing for the projecting portion 68 of the hub 49 of the impeller 42. The impeller 42 and impeller 44 are centrally bored to receive the shaft 26 to which they are keyed by means of Woodrufi key 70. Impeller 44 is counterbored as at 72 to accommodate a retaining washer 74 and nut 76 which threadedly engages the end of shaft 26, and secures the impellers 42 and 44 in assembled relationship upon the shaft 26.

As seen in Fig. 1, the annular rotor housing member 14 is provided with an external boss 80, extending from the outer periphery thereof. Boss 80 is bored to provide an inlet -81 (Fig. 5) into the impeller chamber 34, and is internally threaded to receive a pipe 83 supplying a stream of liquid to be mixed. Housing member 16 likewise has an external peripheral boss 84 bored to provide an outlet from impeller chamber 36, and internally threaded to receive a pipe 87, through which the thoroughly mixed liquid is delivered. The sections 14 and 16 preferably are assembled so that the inlet boss 80 is angularly spaced from the outlet boss 84, as shown in Fig. 2.

The bafile member 28 has a pair of peripheral recessed portions. which provide an upstanding annular rib 88 (Fig. 3), which in co-operation with annular flanges 90 and 92 on the respective housing members 14 and 16, provide an interlock effectively sealing these members against leakage upon tightening of the nuts 32 upon the bolts 30. Generally, the assembly may be drawn sufficiently tight in this manner to prevent leakage, but it will be understood that gaskets may be utilized between these members as well as between the other housing sections.

The. baffie member 28, as best observed in Figs. 3 and 4, is provided with an aperture 98 to permit a flow of fluid. from the, first impeller or mixing chamber 34 to the second, chamber 36, when the device is in operation. The; aperture 98 serves as the sole outlet for mixing chamber 34 and as the sole inlet for mixing chamber 36. A fluidt stream to be mixed is forced through the mixing chambers 34 and 36 and through aperture 98 at a rate determined by the rate of flow of the fluid through supply pipe 83 to inlet passage 81. This rate of flow may be fixed by use of a constant delivery pump (not shown) in the supply system including pipe 83. However, the degree of mixing in the mixer is in part dependent upon the size and location of the aperture 98. It will beseen that the aperture 98 acts as a restricting orifice, the diameter of such orifice in part determining the velocity of flow of the fluid stream from chamber 34 to chamber 36. The velocity of flow through the aperture 98 is also determined by the effective open area of the aperture during the course of a revolution of the impellers 42 and 44, i.e. by the portion of such revolution during which the aperture 98 is uncovered. Thus, the closer the radial spacing of the aperture 98 to the axis of rotation of the impellers, the greater will be the portion of a revolution of such impellers that the aperture 98 is covered by the impeller vanes, and the greater will be the velocity of fluid flow through the aperture 98 while uncovered. Accordingly, the degree of turbulence and mixing action in the mixer 10 is increased by utilizing smaller aperture sizes and closer radial spacing from the axis of impeller rotation. However, optimum size and spacing of the aperture 98 are also determined by the power requirements for forcing the fluid through the mixer. It is preferable that such power requirements be reduced to the minimum commensurate with adequate mixing action. It will also be noted that the degree of pumping action effected in the second mixing chamber 36 is dependent upon the radial spacing of the aperture 98 from the axis of impeller rotation. Thus, the pumping action-in this chamber 36 is at a maximum when aperture 98 is near the axis of rotation.

In general, it has been found that optimum condi-. tions are obtained by spacing the center of the aperture 98 from the central axis of the mixer a distance L (Fig. 4) about two-thirds of the maximum radial dimension M of the respective mixing chambers. The diameter of the aperture 98 may be about one-quarter to one-half the dimension L. For example, in a mixer having a maximum mixing chamber radial dimensions M of 3% inches, the center of the aperture 98 may be at a distance L of about 2 inches from the mixer central axis. The diameter of the aperture 98 may in such a mixer be in a range of from about /2 to 1% inches with satisfactory operation. The diameter of the aperture 98 in the baflie member is preferably 1" for a flow rate of 11 g.p.m.

The aperture 98 is located on a radius preferably midway between the radial extensions of the bosses 80 and 84 forming respectively the inlet and outlet for the mixer. Thus, the aperture 98 is angularly spaced as far as possible from inlet passageway 81 in the direction of rotation of the impeller 42 and the outlet from the second mixing chamber 36 is angularly spaced as far as possible from aperture 98 (which constitutes the inlet for this chamber) in the direction of rotation of impeller 44. By this means, all of the fluid entering the first chamber 34 must travel at least the major portion of one revolution around the chamber before passing through aperture 98, and then must travel the major portion of a second revolution in chamber 36 before being discharged from the mixer. It will be understood, however, that portions of the fluid stream may travel a number of revolutions in each of the chambers 34 and 36 intermingling with incoming fluid upon each revolution before finally being discharged.

The impellers 42 and 44, as may be best observed from Figs. 8 and 9, are provided with a plurality of vanes 94, 94a, respectively, extending from the respective hub portions thereof and having a transverse width slightly less than the width of the respective impeller chambers 34 and 36, to provide a total operating clearance between the edges of the vanes and'the respective chamber walls er, for example, .007 to .015. inch. While four vanes;

94, 94a are shown, it will be understood that a greater or smaller number of vanes might also be provided, de pending somewhat upon the size of the mixing unit constructed. Each impeller vane 94, 94a has a circumferentially extending flange 96, 96a upon its leading edge which is inclined as shown to provide an axial thrust upon the liquid as the impellers turn. Thus, as will be noted from Fig. 3, the flange 96 forming the leading edge of the vanes 94 of the impeller 42 are disposed adjacent the face of the cover plate 12, tending to force the liquid (oil and caustic) entering chamber 34 throughthe inlet pipe 83 in an axial direction as the impeller 42 revolves in a counterclockwise direction to provide a swirling motion and eventually force such liquid through the opening 98 in baifle member 28. The leading edges 96a of the vanes 94a of the second impeller 44 are likewise disposed adjacent the face of the baffle member 28, and tend to exert an axial thrust upon the liquid entering chamber 36 through opening 98. Liquid to be mixed is forced into the chamber 34 through inlet pipe 83 and delivered by impeller vanes 94 through the opening 98, where it is then picked up by the impeller vanes 94a, and finally delivered to the outlet pipe 87, such delivery being facilitated by the centrifugal action of the second impeller 44 in the chamber 36.

In order to provide the novel mixing action of the present invention whereby the stream of oil and caustic may be intimatelyadmixed to disperse the caustic thoroughly in the oil without shearing or homogenizing action, the internal peripheries of each of the impeller housing sections 14 and 16 are provided with a plurality of staggered inwardly projecting teeth 100 and 102, the disposition of which may be most clearly observed from Fig. 10. Thus, teeth 100 extend approximately /a of the way across the inner periphery of the housing member from one side thereof, whereas alternately interspersed teeth 102 extend approximately /3 of the way across the periphery of the housing section from the other side thereof. In a mixer having a chamber of a maximum radial dimension of 3% inches, the teeth may have a height of about /2 inch from base to apex. The clearance between the ends of the impeller vanes 96, 96a respectively, and the apex of the mixing teeth 100, 102 may be about the same as the total clearance between the impeller vanes and side walls, a clearance of .015 to .007 being satisfactory. The angle between the surfaces of the individual teeth, as for example between the surfaces 104 and 106 (Fig. 10) may be, for example, about to However, this angle may be varied to obtain varying degrees of turbulence in the mixer. It will also be understood that the distance to which the teeth extend across the periphery of the housing sections may be varied as desired. However, it is preferable that there be a substantial degree of overlapping of the alter: nate teeth.

By such arrangement, the fluid stream carried by the' impellers 42 and 44 is directed against the inclined faces 104 of the staggered teeth and 102, and such stream, as it is advanced around the mixing chambers, follows a zig-zag path with rapid reversal of direction of flow as indicated by the dashed line in Fig. 10. It will be noted that such flow is back and forth transversely with respect to the axis of rotation of the impellers, with such reversal of direction of transverse flow being effected by the overlapping teeth. It will be understod, of course, that such action sets up a turbulent flow pattern, and that the entire fluid stream is subjected to the peripheral mix ing operation in the course of its travel through the mixing chambers. The staggered arrangement of the peripheral teeth is one of the important factors contributing to intimate mixing without shearing action.

In order to provide a further degree of turbulence of the fluid passing through the mixer, and further ensure that all portions of the fluid stream are subjected to circulating and mixing action, at least one'face of the bafllc member 28 may be provided with a plurality of mixing grooves, such as the two sets of grooves 110 and 112 respectively, best shown in Fig. 4. While the mixing grooves provide improved mixing operation, it will be understod that the invention is not limited to mixers with such gooves, and that mixers utilizing a smooth bafile wall and incorporating the other features of the invention represent an improvement over known types of mixers for the purpose described.

In order to increase the degree of turbulence with such grooves, the forward faces 114 and 114a respectively of the grooves 110 and 112 (with respect to the general direction of fluid flow) may be inclined at a different angle, with respect to the plane surface 116 of the baflie member 28, than are the rear faces 118 and 118a respectively. Thus, as may be more clearly seen from Figs. 6 and 7, the forward faces 114 of the grooves 110 are disposed at a greater angle with respect to the plane face 116 of the baffle 28 than are the rear faces 118 of such grooves, 114:: of the grooves 112 are inclined at a greater angle with respect to such plane surface 116 than are the rear faces 118a. For example, in the device as illustrated, the angle that the faces 114 make with the surface 116 is about 127, whereas the angle which the face 118 makes with the plane face 116 is about 104. It will be understood, of course, that such angles may be widely varied to provide different degrees of turbulence and agitation. In a mixer having a maximum chamber radial dimension of 3% inches, the width of the mixing grooves 110 and 112 may be about inch.

The sets of mixing grooves 110 and 112 are generflly disposed in that portion of the baflie member 28 below the aperture 98, and, as shown in Fig. 4, a satisfactory arrangement is provided wherein each set of grooves is perpendicular to an imaginary radius angularly spaced 135 from a radius containing the center of the aperture 98. The respective grooves are elongated to approximately the maximum radial dimension M of the mixing chamber 34, with the inner three grooves of each set terminating at an imaginary line passing through the center of the aperture 98 and the center of the mixing chamber. Due to the incline of the angle of the grooves with respect to the direction of travel of the fluid through the mixing chamber and the general configuration of the grooves there is no sharp impact of shearing surfaces which would tend to break up the oil globules and cause emulsification. However, a very efficient circulating and mixing action is accomplished, which ensures that all portions of the fluid reach the peripheral teeth for additional action.

While the mixing grooves are shown only in the face of the baflie member 28 in the first mixing chamber 34, it will be understood that similar sets of grooves may be provided in the face of the end wall 18 forming the second mixing chamber. Alternatively, the bafiie mem ber 28 may be provided with mixing grooves on both faces, so as to provide mixing action in both the first and second chambers. It will be further understood that the mixing grooves may be omitted and that the baffle wall 28 may have relatively smooth faces.

The novel mixing apparatus is particularly well adapted to disperse relatively small proportions of strong sodium hydroxide solution into a glyceride oil in a rerefining operation such as that disclosed in Clayton Reissue Patent 23,680, reissued July 7, 1953. For example, a stream of cottonseed oil previously refined by a continuous soda ash process may be combined in proportions of about /2 percent to 3 percent by weight of the oil with a stream of an aqueous solution of sodium hydroxide having a concentration in the range of Baum to 50 Baum. The combined streams are introduced into the mixer of the present invention at a temperature preferably between about 70 and 100 F., wherein they are subjected to intensive mixing by the action of the imand, likewise, the forward faces pellers and mixing surfaces. Such impellers preferably operate at speeds above 1000 r.p.m. and speeds of 1750 r.p.m. to 3400 r.p.m. have been satisfactory. The retention time in the mixing chambers is only about one second, and the temperature rise is relatively small, usually less than one or two degrees Fahrenheit. The relatively low temperature rise is indicative of the low energy requirement in the mixing operation. The thoroughly dispersed mixture delivered from the mixing apparatus is then passed through the heating coil of a heat exchanger, and then to a centrifugal for dilution and separation into an aqueous phase and a purified oil. The decoloration reaction takes place primarily after the mixing action, and a time of, for example, several minutes between mixer and centrifugal may be required, particularly in the case of diflicultly bleached cottonseed oils. In the case of the present mixing apparatus in the process described, a reduction in bleach of as much as one (1) red or more on the Lovibond color scale, 5% column may be obtained as compared with conventional mixing means. Oil losses in such operations are low, generally in the order of 0.2 percent to 0.4 percent.

For example, a crude cottonseed oil having a cup bleach of 35 yellow-2.7 red, by the Oflicial Method of the American Oil Chemists Society, was soda ash-refined according to the processes of Clayton US. Patents 2,190,- 593 and 2,190,594, and re-refined with 2.0% of 20 B. caustic soda solution according to Clayton Reissue No. 23,680. When the caustic and oil were mixed in the mixer of this invention (2 mixers in parallel, 4-tankcar-aday capacity plant) during the re-refining operation, the re-refined oil when water-washed and vacuum-dried in the conventional manner, had a bleach color of 20 yellow-2.0 red. The same crude oil treated exactly the same except that the mixing in the re-refining step was in conventional mixers gave a refined oil that had a bleach color of 35 yellow--2.5 red. The mixer of the invention provided a more rapid, uniform and more efiicient dispersion of the caustic in the oil that resulted in a 0.5 red lower bleach than the conventional mixer.

The mixers used in the foregoing example each had a capacity of .229 gallon for the two mixing chambers. The throughput was at a flow rate of 11 gallons per minute per mixer, resulting in a residence time in the mixing chambers of approximately 1% seconds. The aperture in the baflie between the mixing chambers was one inch in diameter.

The reduction in color and bleach over conventional mixers will depend on the character of the crude oil. Very poor quality crude oils from special or damaged seeds or meats have high colors and bleaches. The bleaches of the refined oil from these crude oils when using the mixers of this invention for dispersing the caustic solution in the oil will be lower by more than 1.0 red than bleaches of these oils that are refined by employing conventional mixers.

It will be understood that if more intensive mixing is required, two or more mixers may be used in series. The through-put through each mixer may in such instance be at a higher rate, for example, to provide a total mixing time of only one or two seconds. It will also be understood that the manner of treating the oil-caustic dispersion delivered from the mixer to effect reaction of the caustic with the color impurities and separation of the purified oil may follow any of the known procedures with general improvement in overall result, due to the intimate dispersion of the caustic in oil without signifiant formation of a stable emulsion or conversion of the neutral oil into soap.

While the mixing apparatus of the invention have been described in relation to alkali re-refining operations for color reduction of glyceride oils, the invention is not limited thereto, but can be employed for the mixing of alkaline refining agents such as soda ash and ammonium hydroxide with crude fatty oils, and in general may be utilized to efiect improvements in the mixing of two or more fluids in any instance in which it is desirable to accomplish rapid and thorough continuous mixing.

While the preferred embodiments of the invention have been described herein, it is understood that the details thereof may be varied within the scope of the following claims.

I claim:

1. A fluid mixer, comprising: a housing providing walls defining a generally cylindrical mixing chamber; a shaft rotatably mounted in said housing and extending into said mixing chamber; a rotary impeller in said chamber mounted on said shaft, said impeller having radial vanes extending across said chamber with only slight operating clearance between said vanes and chamber walls; a fluid inlet in said housing; and a fluid outlet in said housing angularly spaced from said fluid inlet; the inner periphery of said housing comprising a series of teeth extending into said mixing chamber, alternate teeth of said series extending only a part of the way across said mixing chamber from opposite sides of said chamber and being in overlapping relation, the impeller periphery being slightly spaced'uniformly from all of said teeth whereby fluid turbulence adjacent the periphery of said mixing chamber is accomplished without substantial shearing action. 2. The fluid mixer as defined in claim 1, wherein said teeth are of triangular configuration.

3. The fluid mixer as defined in claim 1, wherein said teeth are of triangular configuration with the apex of such triangle being approximately in the range of 80 to 90.

4. The fluid mixer as defined in claim 1, wherein at least one interior side wall of the housing forming the mixing chamber is provided with a plurality of mixing grooves.

5. The fluid mixer as defined in claim 4, wherein said mixing grooves are elongated in a direction substantially perpendicular to a radius of said mixing chamber.

6. A fluid mixer as defined in claim 4, wherein each of said mixing grooves is approximately triangular in cross-section, the base of said triangle forming the mouth of said groove, and the legs of said triangle extending at different angles from said base.

7. The fluid mixer as defined in claim 1, wherein said impeller comprises a plurality of radially extending vanes and each of said vanes is provided with an inclined leading edge to impart an axial thrust upon the fluid to be mixed.

8. A fluid mixer, comprising: a pair of end housing members; a pair of annular housing members intermediate said end housing members; a dividing wall interleaved between said annular housing members; means securing said housing members and dividing wall in assembled relationship, said housing members and wall defining a pair of mixing chambers; a shaft rotatably mounted in at least one of said end housing members and extending through said mixing chambers and said dividing wall; a pair of rotary impellers mounted upon said shaft, said impellers being disposed in said mixing chambers and having radial vanes extending across the respective mixing chambers with only slight operating clearance between said vanes and the chamber walls; fluid inlet means in one of said annular housing members and communicating with the first of said mixing chambers; fluid outlet means in the other of said annular housing members and communicating with the second of said mixing chambers; said dividing wall having a passageway for fluid flow from said first mixing chamber into said second mixing chamher, said fluid inlet and fluid outlet being angularly spaced and said passageway in said dividing wall being disposed intermediate said fluid inlet and fluid outlet.

9. The fluid mixer defined in claim 8, wherein said passageway for fluid from said first mixing chamber to said second mixing chamber is an aperture having its center spaced from the central axis of the mixing chanibers'a distance about two-thirds of the maximum radial dimension of said mixing chambers and located on a radius approximately midway between the angularly spaced fluid inlet and fluid outlet.

10. The fluid mixer as defined in claim 9, wherein said aperture in the dividing wall between the mixing chambers has a diameter in the range of from approximately one-quarter to one-half the distance of the center of said aperture from the central axis of the mixing chambers.

11. The fluid mixer as defined in claim 8, wherein said annular housing members are provided on their internal peripheries with inwardly projecting teeth and wherein said impellers are spaced slightly from said teeth whereby fluid turbulence is effected without substantial shearing action.

12. The fluid mixer as defined in claim 11, wherein said teeth are approximately triangular in configuration and are disposed in overlapping relation with a free space between one end of each of said teeth and a side wall of the mixing chamber.

13. The fluid mixer as defined in claim 8, wherein at least one surface of said dividing wall is provided with a plurality of mixing grooves.

14. The fluid mixer as defined in claim 8, wherein the surface of said dividing wall defining said first mixing chamber is provided with a plurality of mixing grooves elongated in a direction substantially perpendicular to a radius of said mixing chamber.

'15. The fluid mixer as defined in claim 14, wherein two sets of said mixing grooves are provided and wherein said sets of grooves are inclined with respect to each other at an angle of approximately 16. The fluid mixer as defined in claim 8, wherein said impellers each comprise a plurality of vanes and said vanes are provided with inclined leading edges to impart an axial thrust upon the fluid to be mixed.

17. A fluid mixer, comprising: a pair of end housing members, one of said members including a motor housing section; a motor in said motor housing section; a pair of annular housing members intermediate said end housing members; a dividing wall interleaved between said annular housing members; means securing said housing members and dividing wall in assembled relationship, said housing members and dividing wall defining a pair of mixing chambers; said motor having a shaft extending through said one of said end housing members including said motor housing and through the first of said mixing chambers and said dividing wall and terminating in the second of said mixing chambers; a pair of rotary impellers mounted on said shaft, said impellers being disposed in said mixing chambers and having radial vanes extending across the respective mixing chambers with only slight operating clearance between said vanes and the chamber walls; means providing a fluid seal between said shaft and said one of said end housing members through which said shaft extends; fluid inlet means in the annular housing member defining the first of said mixing chambers; fluid outlet means in the annular hous ing member defining the second of said mixing chambers; means in said dividing wall providing a passageway for fluid flow from said first mixing chamber into said second mixing chamber; said inlet means, outlet means, and passageway being positioned and arranged so that fluid entering said inlet means is forced by the impeller in said first chamber to travel for a substantial portion of a revolution through said first chamber, is then delivered into said second chamber, and is forced by the impeller therein to travel through a substantial portion of a second revolution before it is delivered through said outlet; said annular housing members having inner pe ripheral portions extending into said mixing chambers for effecting fluid turbulence.

18. The fluid mixer defined in claim 17, wherein said impellers are provided with means to exert an axial thrust aaaaaar 11 upon the fluid driven thereby and wherein at least one side wall of said mixing chambers is provided with means for effecting turbulence of the fluid forced against such wall by one of said impellers.

19. Apparatus for mixing fluids, comprising: means providing peripheral and side walls defining a generally cylindrical mixing chamber; a shaft rotatably mounted in a side wall of said means and extending into said mixing chamber; a rotary impeller in said chamber mounted on said shaft, said impeller having radial vanes extending across said chamber with only slight operating clearance between said vanes and said chamber side walls; a wall of said chamber having an inlet for introduction into said mixing chamber of fluids to be mixed; and a side wall of said chamber having an outlet orifice angularly spaced from said inlet for restricted passage of mixed fluids from said mixing chamber; the peripheral walls of said mixing chamber having a series of teeth extending into said mixing chamber, alternate teeth of said series extending only a part of the way across said mixing chamber from opposite sides of said chamber and being in overlapping relationship, the impeller periphery being slightly spaced uniformly from all of said teeth whereby fluid turbulence adjacent the periphery of said mixing chamber is accomplished without substantial shearing action.

20. Apparatus for mixing fluids, comprising: a housing defining a pair of adjacent generally cylindrical mixing chambers, said mixing chambers being separated by a dividing wall; a shaft rotatably mounted in said housing and extending through said mixing chambers and said dividing wall; a pair of rotary impellers mounted upon said shaft, said impellers being disposed in said mixing chambers and having radial vanes extending across said mixing chambers with only slight operating clearance between said vanes and the chamber walls; inlet means through said housing for introducing a fluid to be mixed into one of said mixing chambers; outlet means through said housing for withdrawing mixed fiuid from the other of said mixing chambers; said dividing wall having an orifice for restricted passage of fluid from the first chamber to the other of said mixing chambers, said inlet means and said outlet means being angularly spaced and said orifice in said dividing wall being disposed intermediate said inlet means and outlet means; a series of teeth extending from the inner periphery of said housing into each mixing chamber, alternate teeth of said series extending only part of the way across a mixing chamber from opposite sides of said chamber and being in overlapping relation, the impeller periphery being slightly spaced uniformly from all of said teeth whereby fluid turbulence adjacent the periphery of said mixing chamber is accomplished without substantial shearing action.

References Cited in the file of this patent UNITED STATES PATENTS 8,841 McKinlay Mar. 30, 1852 48,449 Sanborn Ian. 27, 1865 812,122 Fassett Feb. 6, 1906 2,053,876 Pfau et al. Sept. 8, 1936 2,066,621 Gray Jan. 5, 1937 2,507,184 Rini May 9, 1950 2,512,245 Fash June 20, 1950 2,645,464 Forbes July 14, 1953 2,726,851 Krupp et al. Dec. 13, 1955 

